It is well-known that thermoplastic polymers may be colored by adding pigments or solvent dyes (e.g., see Thomas G. Weber, Editor, Coloring of Plastics, John Wiley & Sons, New York, 1979). The use of pigments, however, is accompanied by undesirable properties such as opacity, dullness of color, low tinctorial strength, etc. Also, difficulties in uniformly blending the insoluble pigments with the thermoplastic resin are often encountered. Also useful for coloring thermoplastic polymers are the solvent dyes (K. Venkataraman, Editor, The Chemistry of Synthetic Dyes, Vol. 8, Academic Press, New York, 1978, pp. 81-131), which provide compositions having improved clarity, brightness in hue and high tinctorial strength, but which may lead to dye migration, extraction, etc. from the colored thermoplastic polymer. These problems are of particular concern when solvent dyes are used to color flexible polymers such as polyvinyl chloride, polyethylene and polypropylene which have low glass transition temperatures.
It is also known that one can prepare solvent soluble nonextractable polymeric aminotriaryl methane dyes having polyester, polycarbonate, polyurethane, or polyethyleneimine backbones and incorporate them into polymers such as polyvinyl choride, polyvinylidene chloride and acrylic polymers such as poly(methyl methacrylate) etc. by solvent blending techniques [U.S. Pat. No. 4,477,635 (1984)]. Difficulties are encountered in preparing these polymeric colored compounds because a non-colored intermediate aromatic amine containing polymer must be prepared and then the aromatic amine moiety in the polymer structure must be converted into an aminotriarylmethane moiety by further reaction with a diaryl ketone in the presence of a condensation catalyst such as phosphorous oxychloride, in an inert organic solvent. Attempts to make colored polyester compositions in one step by copolymerizing aminotriarylmethane colorants containing reactive groups generally fail, presumably because of the thermal instability of the triarylmethane chromophore. These previously disclosed polymeric aminotriarylmethane compositions also have poor fastness to light and do not have the requisite thermal stability for use in coloring thermoplastic polymers via the more favorable method of high temperature melt blending.
It is further known that one may color plastics, in particular polyolefins, with low melting, cross-linked colored polyester compositions containing residues of terephthalic acid, isophthalic acid, or both, a low-molecular weight trimethylol alkane, i.e., 1,1,1-trimethylol propane and a copolymerizable colorant, said colorant being present at a level of 0.1-25% by weight (U.S. Pat. No. 4,116,923). Difficulties are encountered, however, in preparing these highly cross-linked colored polymers as extreme care with regard to the temperature, amount of vacuum, the level of colorant present, and the reaction time, is necessary in order to attempt to reproduce the same quality of cross-linked colored polyester composition. Further, these colored polyester compositions are brittle or low melting and may cause deterioration in physical properties of thermoplastic polymers when added in quantities sufficient to produce a high level of coloration. Critical in the preparation of these previously disclosed polymers is the achievement of a low degree of polymerization to give a low melting polymer which has adequate solubility characteristics in the polymer to be colored; however, to accomplish this the colorant may not be copolymerized, paricularly when added at high levels, thus leading to undesirable extractable colorants.
It is also known to color thermoplastic polymeric materials using color concentrates consisting of physical admixtures of polymers and colorants. However, the use of such physical admixtures to color polymeric materials such as polyesters, e.g., poly(ethylene terephthalate) and blends thereof, present a number of problems:
(1) Colorant migration during drying of the colored polymer pellets. PA1 (2) Colorant migration during extrusion and colorant accumulation on dies which can cause film rupture and shut-downs for clean up, etc. Such colorant migration and accumulation result in time consuming and difficult clean-up when a polymer of another color is subsequently processed in the same equipment. PA1 (3) Colorants may not mix well, for example, when using two or more color concentrates to obtain a particular shade. PA1 (4) Colorants may diffuse or exude during storage of the colored polymeric material.
Furthermore, the presence of oligomeric material in the polymers, such as polyester, admixed with the colorants to produce the known color concentrates can cause problems of equipment contamination during processing.
As noted above, inorganic and low molecular weight organic compounds are widely used as colorants for polymeric materials. By proper combination of colors, nearly any color can be generated. However, there are problems with this coloration system, including chemical incompatibility between the colorant and polymer and the carcinogenic and/or toxic nature of many of the colorants. Of particular concern in the injection molding of polyesters and blends of polyester and polycarbonate is the appearance of a discolored, dark streak at weld lines. Weld lines are typically formed in an injection molded part whenever two advancing melt fronts meet. This problem is particularly severe when dark reds and greens are desired. Because these discolored weld lines are unacceptable in aesthetic applications, these materials often cannot be used in large parts which require multiple gates.
Further, U.S. Pat. Nos. 4,267,306; 4,359,570; 4,403,092; and 4,617,373; describe the preparation of colored polyester compositions by copolymerization of thermally stable colorants during the polyester preparation. However, since the colorants are exposed to very high temperatures for prolonged periods of time necessary for polyester formation, only very stable colorants are suitable, thus severely circumscribing the selection of efficacious colorants. For example, only the non azo type colorants have been shown to have the adequate thermal stability for copolymerization into polyesters; azo type compounds lack the requisite thermal stability for copolymerization into polyesters.
Further, Japanese Kokoku Patent No. Sho 48 [1973] 8562 describes polymeric urethane compositions derived from aliphatic and aromatic diisocyanates and colorants containing two hydroxy groups attached to aromatic rings. However, extreme reaction conditions are required to react the aromatic hydroxy groups completely and the colored polymers prepared from aromatic diols and diisocyanates have limited solubility in the preparative reaction solvents and in thermoplastic resins.
We have discovered novel light-absorbing polyurethane compositions which have light absorbing moieties from various chromophore classes, including the broad range of easily-obtained and relatively inexpensive azo colorants copolymerized therein. These light-absorbing compounds can be copolymerized into polyurethane under sufficiently mild conditions, so as to not destroy the chromophoric moiety; the colored polyurethane compositions thus provided can then be used to impart color, ultraviolet and/or near infrared light absorbing properties to other thermoplastic polymers (e.g., polyesters) to provide colored thermoplastic polymer compositions in a wide ranged of colors either with or without UV or infrared light-absorbing properties.